U.S. patent number 6,369,292 [Application Number 08/994,530] was granted by the patent office on 2002-04-09 for absorbent articles having reduced outer cover dampness.
This patent grant is currently assigned to Kimberly-Clark Worldwide, Inc.. Invention is credited to Timothy Ray Martin, Ann Louise McCormack, David Craige Strack.
United States Patent |
6,369,292 |
Strack , et al. |
April 9, 2002 |
**Please see images for:
( Certificate of Correction ) ** |
Absorbent articles having reduced outer cover dampness
Abstract
Absorbent articles having reduced outer cover dampness are
provided and include a hydrophobic barrier layer positioned between
an absorbent core and a breathable liquid impervious outer cover.
The hydrophobic barrier layer, such as one or more layers of
nonwoven webs, has a thickness of at least 0.03 cm and a hydrohead
value of at least 18 millibars. The hydrophobic barrier layer does
not significantly reduce the water-vapor transmission rate (WVTR)
of the absorbent article when the absorbent core is dry yet
significantly reduces the overall WVTR of the absorbent article
once the absorbent core is wet. Thus, an absorbent article is
provided having a WVTR that exceeds about 1500 grams/square meter
24 hours when dry and yet is less than 15,000 grams/square meter 24
hours when wet.
Inventors: |
Strack; David Craige (Canton,
GA), McCormack; Ann Louise (Cumming, GA), Martin; Timothy
Ray (Alpharetta, GA) |
Assignee: |
Kimberly-Clark Worldwide, Inc.
(Neenah, WI)
|
Family
ID: |
26708623 |
Appl.
No.: |
08/994,530 |
Filed: |
December 19, 1997 |
Current U.S.
Class: |
604/370; 604/372;
604/378; 604/385.01 |
Current CPC
Class: |
A61F
13/51462 (20130101); A61F 13/5148 (20130101); D04H
3/16 (20130101); B32B 5/022 (20130101); B32B
5/26 (20130101); B32B 2555/02 (20130101) |
Current International
Class: |
B32B
5/26 (20060101); B32B 5/22 (20060101); A61F
13/15 (20060101); D04H 3/16 (20060101); D04H
13/00 (20060101); A61F 013/15 (); A61F
013/20 () |
Field of
Search: |
;604/367,370,372,374-379,385.1,385.01 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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Other References
NRL Report 4364, "Manufacture of Super-Fine Organic Fibers" by V.A.
Wendt et al. .
NRL Report 5265 "An Improved Apparatus for the Formation of
Super-Fine Thermoplastic Fibers" by K.D. Lawrence et al..
|
Primary Examiner: Weiss; John G.
Assistant Examiner: Reichle; K. M.
Attorney, Agent or Firm: Tulley, Jr.; Douglas H.
Claims
What is claimed is:
1. An absorbent article comprising:
an outer cover comprising a liquid impervious film and wherein the
outer cover has a WVTR over 1500 g/m.sup.2 /24 hours;
a liquid pervious topsheet;
an absorbent body situated between said outer cover and said
topsheet; and
a hydrophobic porous barrier layer having a WVTR over 1500
g/m.sup.2 /24 hours, a hydrohead value of at least 18 cm and a bulk
of at least about 0.03 cm and situated between said outer cover and
said absorbent body, said porous barrier layer comprising a
hydrophobic fibrous material selected from the group consisting of
nonwoven webs and woven fabrics and further wherein said outer
cover and porous barrier layer collectively have an inverted-WVTR
of less than about 15,000 g/m.sup.2 /day.
2. The absorbent article of claim 1 wherein said fibrous material
comprises polyolefin fibers.
3. The absorbent article of claim 2 wherein said outer cover
comprises a multilayer laminate and wherein said multilayer
laminate comprises said liquid impervious film and at least one
nonwoven web.
4. The absorbent article of claim 3 wherein said fibrous material
comprises at least one meltblown fiber nonwoven web.
5. The absorbent article of claim 4 wherein said porous barrier
layer has a basis weight between 16 g/m.sup.2 and about 64
g/m.sup.2.
6. The absorbent article of claim 5 wherein the liquid impervious
film comprises a microporous film.
7. The absorbent article of claim 3 wherein said fibrous material
comprises a meltblown fiber nonwoven web and a spunbond fiber
nonwoven web.
8. The absorbent article of claim 7 wherein said porous barrier
layer has a basis weight between 16 g/m.sup.2 and about 64
g/m.sup.2.
9. The absorbent article of claim 8 wherein the liquid impervious
film comprises a microporous film and further wherein said porous
barrier layer has a hydrohead value of at least 30 cm.
10. The absorbent article of claim 9 wherein said meltblown layer
is adjacent said absorbent core.
11. The absorbent article of claim 3 wherein said fibrous material
comprises first and second spunbond fiber nonwoven webs and at
least one meltblown fiber nonwoven web situated between said first
and second spunbond fiber nonwoven webs.
12. The absorbent article of claim 3 wherein said porous barrier
layer extends under substantially the entire portion of said
absorbent body.
13. The absorbent article of claim 12 wherein the absorbent article
has as its longest dimension a length when in a flat, uncontracted
state and further wherein the porous barrier layer is centrally
located within the absorbent article and extends lengthwise within
the absorbent article.
14. The absorbent article of claim 3 wherein the porous barrier
layer comprises a plurality of polyolefin fiber nonwoven webs and
wherein said plurality of nonwoven webs have a hydrohead of at
least about 30 mbar and a basis weight in excess of about 20
g/m.sup.2.
15. The absorbent article of claim 14 wherein said outer cover and
said barrier layer have a WVTR over 1500 g/m.sup.2 /day and an
inverted-WVTR of less than 12,000 g/m.sup.2 /day.
16. The absorbent article of claim 15 wherein said barrier layer
has a WVTR of at least 3000 g/m.sup.2 /day.
17. The absorbent article of claim 3 wherein said barrier layer has
a hydrohead of at least 30 cm and comprises a layer of meltblown
fibers and a layer of spunbond fibers and wherein said
liquid-imperious outer cover and said barrier layer have a WVTR
over 4000 g/m.sup.2 /day and an inverted-WVTR of less than about
12,000 g/m.sup.2 /day.
18. The absorbent article of claim 3 wherein said article comprises
a personal care article.
19. The absorbent article of claim 3 wherein said article comprises
a diaper.
20. The absorbent article of claim 3 wherein said article comprises
an adult incontinence garment.
21. The absorbent article of claim 1 wherein said fibrous material
comprises a meltblown fiber nonwoven web and wherein said porous
barrier layer has a basis weight over 16 g/m.sup.2.
22. The absorbent article of claim 1 wherein said fibrous material
comprises a meltblown fiber nonwoven web and a spunbond fiber
nonwoven web.
23. The absorbent article of claim 22 wherein said said porous
barrier layer has a basis weight in excess of about 20
g/m.sup.2.
24. The absorbent article of claim 23 wherein said article
comprises a personal care article.
25. The absorbent article of claim 23 wherein said article
comprises a diaper.
26. The absorbent article of claim 23 wherein said article
comprises an adult incontinence garment.
27. The absorbent article of claim 1 having a wrap sheet about said
absorbent body wherein the absorbent body has a first side and a
second side opposite said first side and further wherein said
wrapsheet comprises a hydrophobic nonwoven portion extending over
the first side of said absorbent body and a hydrophilic nonwoven
portion extending over the second side of said absorbent body and
further wherein said hydrophilic nonwoven portion is adjacent said
topsheet.
28. The absorbent article of claim 1 wherein said porous barrier
layer has a hydrohead value of at least about 30 cm and a basis
weight in excess of about 20 g/m.sup.2 and wherein said outer cover
and said barrier layer have a WVTR over 3500 g/m.sup.2 /day and an
inverted-WVTR of less than about 12,000 g/m.sup.2 /day.
Description
TECHNICAL FIELD
The present invention relates to absorbent articles. More
particularly, the present invention relates to absorbent articles,
such as personal care products, that have reduced outer cover
dampness.
BACKGROUND OF THE INVENTION
Absorbent articles, such as infant diapers, adult incontinence
garments, sanitary napkins, bedpads, panty liners, incontinent
pads, and the like are well known in the art. These articles are
inexpensive, often disposable, and yet capable of absorbing and
retaining fluids and other bodily discharges. These absorbent
articles typically have an outer cover having a liquid-impermeable
plastic film, such as polypropylene and/or polyethylene, to prevent
the retained discharge from leaking from the article and soiling
items of clothing, bedding, furniture, and the like. However, until
recently liquid-impermeable outer covers often employed a film
which was impervious to water vapor as well as liquids. Because the
outer cover was impermeable to both liquids and water vapor, the
absorbent article often felt hot and clammy to the wearer even
prior to absorbing any bodily discharge. Furthermore, this lack of
permeability to water vapor often caused irritation of the skin and
in some cases severe dermatological problems. For example,
absorbent articles such as diapers may cause diaper rash on infants
when worn for considerable periods of time. In addition to concerns
over skin wellness, the liquid impermeable plastic films employed
as outer covers often lacked the aesthetic and tactile qualities
desired in personal care products such as disposable diapers.
In response to the problems described above, breathable cloth-like
liquid-impermeable outer covers have been developed. Such
structures, typically laminates of several different sheets, remain
substantially impervious to liquids but are "breathable" in the
sense that water vapor will pass through the outer cover.
Breathable outer covers have become increasingly popular and more
highly commercialized in absorbent personal care products,
particularly in connection with disposable diapers. However, while
providing a healthier and more comfortable product from the
wearer's perspective, breathable liquid-impervious outer covers
often suffer from an unwanted and unpleasant outer cover dampness.
Continued use of an absorbent article after fluid has been
discharged and absorbed by the article can, even after a short
time, cause the outer cover to develop a wet or damp feel. However,
this unpleasant wet feeling is not typically due to permeation of
liquid through the liquid-impermeable cover or leakage from the
article but is simply condensation of water vapor on the outer
cover as a result of excess water vapor passing through the outer
cover.
Thus, there exists a need for an absorbent article which allows
sufficient water vapor permeation for absorbent articles to remain
a healthy and comfortable product for the wearer but which does not
allow excessive water vapor permeation after discharge of fluid
into the article such that the outer cover develops a wet or damp
feel.
SUMMARY OF THE INVENTION
The present invention addresses the difficulties and problems
discussed above as well as problems experienced by those skilled in
the art by providing an absorbent article comprising: (a) a
breathable liquid-impervious outer cover; (b) a liquid pervious
topsheet; (c) an absorbent body between the outer cover and
topsheet; and (d) a hydrophobic barrier layer positioned between
the breathable outer cover and the absorbent body. The hydrophobic
barrier layer can comprise one or more layers of porous material
having a supported hydrohead value at least 18 cm and a bulk of at
least about 0.012 inches (0.03 cm) and further wherein the outer
cover and barrier layer collectively have an inverted-WVTR of less
than about 15,000 g/m.sup.2 /day. Desirably the porous material has
a hydrohead of at least 30 mbar and, still further, comprises a
fibrous material such as a woven fabric or nonwoven web. In a
further aspect, hydrophobic barrier layer can comprise a nonwoven
web having a Frazier air permeability over 20 cubic feet per square
foot per minute. The barrier layer may comprise, in one aspect, one
or more nonwoven webs of meltblown fibers having a collective basis
weight of over 16 g/m.sup.2 (grams per square meter). In still a
further aspect, the barrier layer can comprise a plurality of
layers, including a layer of meltblown fibers, wherein the
plurality of layers have a collective basis weight in excess of
about 20 g/m.sup.2, desirably having a basis weight from about 25
g/m.sup.2 to about 40 g/m.sup.2. In a further aspect, the
hydrophobic barrier layer may comprise at least one spunbond layer
and one meltblown layer.
In a further aspect, the absorbent article includes a hydrophobic
barrier layer that extends under substantially the entire portion
of the absorbent body. For example, the hydrophobic barrier layer
can extend beyond outer edges of the absorbent body or only along
the length of the central portion of the absorbent article. In a
further aspect, the barrier layer may comprise at least in part a
portion of a wrapsheet about the absorbent body. For example, the
wrapsheet can comprise a hydrophobic barrier layer over a first
side of the absorbent body adjacent the outer cover and a
hydrophilic nonwoven layer over the opposed side of the absorbent
body adjacent the topsheet. Alternatively, the wrapsheet can
comprise a continuous sheet having a hydrophobic portion adjacent
the liquid-impervious outer cover and a hydrophilic portion over
the opposed side of said absorbent body and adjacent the topsheet
such that the hydrophobic portion of the wrapsheet comprises at
least part of the hydrophobic barrier layer.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a representative partially cut away plan view of a diaper
of the present invention in a flat, uncontracted state.
FIG. 2 is a cross-sectional side view of an absorbent core and
wrapsheet.
FIG. 3 is a cross-sectional side view of an absorbent core and
wrapsheet.
FIG. 4 and FIG. 5 depict a cross-sectional view of the hydrophobic
barrier sheet.
DEFINITIONS
As used herein the term "nonwoven fabric" or "nonwoven web" means a
web having a structure of individual fibers or threads which are
interlaid, but not in an identifiable manner as in a knitted
fabric. Nonwoven fabrics or webs have been formed from many
processes such as for example, meltblowing processes, spunbonding
processes, hydroentangling, and bonded carded web processes.
As used herein the term "spunbonded fibers" refers to small
diameter fibers which are formed by extruding molten thermoplastic
material as filaments from a plurality of fine, usually circular
capillaries of a spinneret with the diameter of the extruded
filaments then being rapidly reduced such as, for example,
described in U.S. Pat. No. 4,340,563 to Appel et al., and U.S. Pat.
No. 3,692,618 to Dorschner et al., U.S. Pat. No. 3,802,817 to
Matsuki et al., U.S. Pat. Nos. 3,338,992 and 3,341,394 to Kinney,
U.S. Pat. No. 3,502,763 to Hartman, U.S. Pat. No. 3,542,615 to Dobo
et al., U.S. Pat. No. 5,336,552 to Strack et al. and U.S. Pat. No.
5,382,400 to Pike et al. Spunbond fibers are generally not tacky
when they are deposited onto a collecting surface. Thus, webs of
spunbond fibers are commonly treated to impart additional integrity
to the web such as, for example, described in commonly assigned
U.S. patent application Ser. No. 08/362,328 to Arnold et al. filed
Dec. 22, 1994, U.S. Pat. No. 4,374,888 to Bornslaeger, and U.S.
Pat. No. 3,855,046 to Hansen and Pennings. Spunbond fibers are
generally continuous and often have average diameters (from a
sample of at least 10) larger than 7 microns, more particularly,
between about 10 and 50 microns. However, fine fiber spunbond
materials may be produced and, as used herein, include fibers
having a denier of 2 or below.
As used herein the term "meltblown fibers" means fibers formed by
extruding a molten thermoplastic material through a plurality of
fine, usually circular, die capillaries as molten threads or
filaments into converging high velocity, usually hot, gas (e.g.
air) streams which attenuate the filaments of molten thermoplastic
material to reduce their diameter, which may be to microfiber
diameter. Thereafter, the meltblown fibers are carried by the high
velocity gas stream and are deposited on a collecting surface to
form a web of randomly disbursed meltblown fibers. Such a process
is disclosed in various patents and publications, for example, in
U.S. Pat. No. 3,849,241 to Butin et al.; NRL Report 4364,
"Manufacture of Super-Fine Organic Fibers" by V. A. Wendt, E. L.
Boone and C. O. Fluharty; NRL Report 5265, "An Improved Apparatus
for the Formation of Super-Fine Thermoplastic Fibers" by K. D.
Lawrence, R. T. Lukas, and J. A. Young. Meltblown fibers are
generally microfibers which may be continuous or discontinuous and
are generally smaller than 10 microns in average diameter.
As used herein, the term "polymer" generally includes, but is not
limited to, homopolymers, copolymers, such as for example, block,
graft, random and alternating copolymers, terpolymers, etc., and
blends and modifications thereof. Furthermore, unless otherwise
specifically limited, the term "polymer" shall include all possible
geometric configurations of the molecules. These configurations
include, but are not limited to, isotactic, syndiotactic and random
symmetries.
As used herein "multilayer laminate" means a laminate wherein some
of the layers are spunbond and some meltblown such as a
spunbond/meltblown/spunbond (SMS) laminate and others as disclosed
in U.S. Pat. No. 4,041,203 to Brock et al., U.S. Pat. No. 4,374,888
to Bornslaeger, U.S. Pat. No. 5,169,706 to Collier, et al, U.S.
Pat. No. 5,145,727 to Potts et al., U.S. Pat. No. 5,178,931 to
Perkins et al. and U.S. Pat. No. 5,188,885 to Timmons et al. Such a
laminate may be made by sequentially depositing onto a moving
forming belt first a spunbond fabric layer, then a meltblown fabric
layer and last another spunbond layer and then bonding the laminate
in a manner described in the aforesaid references. Alternatively,
the fabric layers may be made individually, collected in rolls, and
combined in a separate bonding step. Multilayer laminates may also
have various numbers of meltblown layers or multiple spunbond
layers in many different configurations and may include other
materials such as films (F) or coform materials, e.g. SMMS, SFS,
etc.
As used herein, the term "coform" means a process in which at least
one meltblown diehead is arranged near a chute through which other
materials are added to the web while it is forming. Such other
materials may be pulp, superabsorbent particles, cellulose or
staple fibers, for example. Coform processes are described in
commonly assigned U.S. Pat. Nos. 4,818,464 to Lau and 4,100,324 to
Anderson et al.
As used herein "point bonding" means bonding one or more layers of
fabric at a plurality of discrete bond points. For example, thermal
point bonding generally involves passing one or more layers to be
bonded between heated rolls such as, for example an engraved
pattern roll and a smooth calender roll. The engraved roll is
patterned in some way so that the entire fabric is not bonded over
its entire surface, and the anvil roll is usually flat. As a
result, various patterns for engraved rolls have been developed for
functional as well as aesthetic reasons. One example of a pattern
has points and is the Hansen Pennings or "H&P" pattern with
about a 30% bond area when new and with about 200 bonds/square inch
as taught in U.S. Pat. No. 3,855,046 to Hansen and Pennings.
Another typical point bonding pattern has square pin bonding areas
wherein each pin has a side dimension of 0.023 inches, a spacing of
0.062 inches (1.575 mm) between pins, and a depth of bonding of
0.033 inches (0.838 mm). The resulting pattern has a bonded area of
about 15% when new. Yet another common pattern is the C-Star
pattern which has, when new, a bond area of about 16.9%. The C-Star
pattern has a cross-directional bar or "corduroy" design
interrupted by shooting stars. Other common patterns include a
diamond pattern with repeating and slightly offset diamonds with
about a 16% bond area. Typically, the percent bonding area is less
than about 50% and more desirably varies from around 10% to around
30% of the area of the fabric laminate web.
As used herein a "superabsorbent" or "superabsorbent material"
refers to a water-swellable, water-soluble organic or inorganic
material capable, under favorable conditions, of absorbing at least
about 20times its weight and, more desirably, at least about 30
times its weight in an aqueous solution containing 0.9 weight
percent sodium chloride. Organic materials suitable for use as a
superabsorbent material in conjunction with the present invention
include, but are not limited to, natural materials such as guar
gum, agar, pectin and the like; as well as synthetic materials,
such as synthetic hydrogel polymers. Such hydrogel polymers
include, for example, alkali metal salts of polyacrylic acids,
polyacrylamides, polyvinyl alcohol, ethylene, maleic anhydride
copolymers, polyvinyl ethers, methyl cellulose, carboxymethyl
cellulose, hydroxypropylcellulose, polyvinylmorpholinone, and
polymers and copolymers of vinyl sulfonic acid, polyacrylates,
polyacrylamides, polyvinylpyrridine, and the like. Other suitable
polymers include hydrolyzed acrylonitrile grafted starch, acrylic
acid grafted starch, and isobutylene maleic anhydride polymers and
mixtures thereof. The hydrogel polymers are preferably lightly
crosslinked to render the materials substantially water insoluble.
Crosslinking may, for example, be accomplished by irradiation or by
covalent, ionic, van der Waals, or hydrogen bonding. The
superabsorbent materials may be in any form suitable for use in
absorbent composites including particles, fibers, flakes, spheres
and the like. Typically the superabsorbent material is present
within the absorbent body in an amount from about 5 to about 95
weight percent based on total weight of the absorbent body.
Superabsorbents are generally available in particle sizes ranging
from about 20 to about 1000 microns. An example of a suitable
commercially available superabsorbent is SANWET IM 3900 available
from Hoescht Celanese located in Portsmouth, Va. and DRYTECH 2035LD
available from Dow Chemical Co. located in Midland, Mich.
As used herein, the term "breathable" means a material which is
permeable to water vapor as measured by the water vapor
transmission test discussed herein below, having a WVTR of at least
1500 g/m.sup.2 /24 hours.
As used herein, the term "personal care product" means diapers,
training pants, absorbent underpants, adult incontinence products,
feminine hygiene products and the like.
DESCRIPTION OF THE INVENTION
Absorbent articles generally include a liquid permeable topsheet,
which faces the wearer, and a liquid-impermeable bottom sheet or
outer cover. Disposed between the topsheet and outer cover is an
absorbent core, often the topsheet and outer cover are sealed to
encase the absorbent core. Although the following detailed
description will be made in the context of a disposable diaper, one
skilled in the art will appreciate that the concepts of the present
invention would also be suitable for use in connection with other
types of absorbent articles, particularly other personal care
products. In addition, although the present invention is described
in the context of several specific configurations, it will be
appreciated that further combinations or alterations of the
specific configurations discussed below may be made by one skilled
in the art without departing from the spirit and scope of the
present invention.
A diaper 10, as shown in FIG. 1, may comprise a liquid-impervious
breathable outer cover 12, a liquid permeable topsheet 14
positioned in facing relation to the outer cover 12, and an
absorbent core 16 between the outer cover 12 and topsheet 14.
Disposed between the absorbent core 16 and the breathable outer
cover 12 is a hydrophobic breathable barrier layer 18.
The diaper 10 may be of various shapes such as, for example, an
overall rectangular shape, T-shape or an hour glass shape. The
topsheet 14 is generally coextensive with the outer cover 12 but
may optionally cover an area which is larger or smaller than the
area of the outer cover 12, as desired. Portions of the diaper 10,
such as a marginal section of the outer cover 12, may extend past
the terminal edges of the absorbent core 16. In the illustrated
embodiment, for example, the outer cover 12 can extend outwardly
beyond the terminal marginal edges of the absorbent core 16 to form
side margins 22 and end margins 24 of the diaper 10.
The topsheet 14, as representatively illustrated in FIG. 1,
preferably presents a body facing surface which is compliant, soft
to the touch, and non-irritating to the wearer's skin. The topsheet
14 is suitably employed to help isolate the wearer's skin from
liquids held in the absorbent core 16. In order to present a dryer
surface to the wearer, the topsheet 14 may be less hydrophilic than
the absorbent core 16 and also sufficiently porous to be readily
liquid permeable. Topsheets are well known in the art and may be
manufactured from a wide variety of materials, such as porous
foams, reticulated foams, apertured plastic films, natural fibers
(i.e., wool or cotton fibers), synthetic fibers (i.e., polyester,
polypropylene, polyethylene, etc.), or a combination of natural and
synthetic fibers. For example, the topsheet may comprise meltblown
or spunbonded web of polyolefin fibers or a bonded-carded web
composed of natural and/or synthetic fibers. In this regard the
topsheet may be composed of substantially hydrophobic material
treated with a surfactant or otherwise processed to impart the
desired level of wettability and permeability. As an example,
surfactant may be applied, in an amount to impart the desired
degree of hydrophilicity, by conventional means, such as spraying,
printing, brush coating or the like. In a preferred embodiment, the
topsheet may comprise a nonwoven web of polypropylene spunbond
fibers or polyethylene/propylene multicomponent spunbond fibers
treated with a surfactant, octylphenoxypolyethoxyethanol,
commercially available from Union Carbide of Danbury, Conn. under
the trademark TRITON X-102.
The backsheet or outer cover 12 may comprise a breathable
liquid-impervious structure and may often comprise a multilayer
laminate. In the particular embodiment shown in FIG. 1, the outer
cover comprises a breathable liquid impervious film 26 and one or
more additional nonwoven layers 28 (shown in FIG. 1 as a single
layer). The particular structure and composition of the outer cover
may be selected from various combinations of films and/or
nonwovens; the nonwovens layers are generally selected for
providing the desired strength, abrasion resistance, tactile
properties and/or aesthetics. In particular, it is preferred that
the outer most portion of the outer cover 12, such as nonwoven
layer 28 as shown in FIG. 1, comprise a durable material having a
cloth-like feel and good abrasion resistance, such as an SMS
laminate. Liquid-impervious outer covers comprising multilayer
laminates having thin non-porous films, such as polyvinyl alcohol,
which allow the migration of water vapor through the film itself
are known in the art. In addition, films which are rendered
breathable, but which remain liquid-impervious, by the formation of
microporous voids sized to allow the transmission of water vapor
therethrough are likewise known in the art. Multilayer laminates
incorporating the latter type of breathable films are generally
preferred. These films may be rendered vapor permeable by adding
filler particles to the film composition and either rolling or
stretching the film causing fractures to form where the filler
particles are located. The amount of filler within the film and the
degree of stretching and/or rolling is controlled to impart the
desired degree of vapor permeability. These films are typically
formed from a polyolefin film, such as polyethylene or
polypropylene. Examples of breathable liquid-impervious films and
liquid-impervious multilayer laminates are disclosed in U.S. Pat.
No. 4,777,073 issued to Sheth, U.S. Pat. No. 4,818,600 issued to
Braun et al., and World Publication No. WO95/16562 and World
Publication No. WO96/19346 and commonly assigned U.S. patent
application Ser. No. 08/929,562 filed Sep. 15, 1997 to McCormack et
al., the entire contents of the aforesaid references are
incorporated herein by reference. A particularly desirable material
for use in liquid impervious breathable multilayer laminates is a
biaxially oriented polyethylene microporous film material which is
about 50 weight percent calcium carbonate and which is commercially
available from Exxon Chemical Co., Inc. of Linden, N.J. under the
trade name EXXAIRE.
Between the breathable liquid-impervious outer cover 12 and the
liquid pervious topsheet 14 is positioned an absorbent core 16
which typically includes superabsorbent particles and, optionally,
additional absorbent materials such as absorbent fibers including,
but not limited to, wood pulp fluff fibers, synthetic wood pulp
fibers, synthetic fibers and combinations thereof. A common problem
with wood pulp fluff, however, is its lack of integrity and a
tendency to collapse when wet. Thus, it is often advantageous to
add a stiffer reinforcing fiber such as polyolefin meltblown fibers
or shorter length staple fibers, typically provided as a coform
material. For example, as indicated above, superabsorbent particles
and/or staple fibers such as wood pulp may be injected into
meltblown fiber stream so as to be entrapped or bonded to the
meltblown fibers. The superabsorbent materials may be substantially
homogeneously mixed with the hydrophilic fibers or may be
selectively placed into desired zones of the absorbent body to
better contain and absorb body exudates. The concentration of the
superabsorbent materials may also vary through the thickness of the
absorbent core. Alternatively, the absorbent core may comprise a
laminate of fibrous webs and superabsorbent materials or other
suitable means for maintaining superabsorbent in localized
areas.
The absorbent core may have any of a number of shapes. For example,
the absorbent core may be rectangular, I-shaped, or T-shaped. It is
generally preferred that the absorbent core be narrower in the
crotch area than in the front or rear portions of the diaper. The
size of the absorbent core and selection of materials therein will
vary with the desired loading capacity, the intended use of the
absorbent article and other factors known to those skilled in the
art.
The absorbent core 16 may, optionally, have a hydrophilic tissue
wrapsheet (not shown in FIG. 1). The tissue wrapsheet helps to
maintain the integrity of some absorbent structures, such as
airlaid fibrous structures. In addition, the tissue wrapsheet also
helps to distribute liquid over the mass of the absorbent body,
particularly when using a material with excellent wicking
properties such as absorbent cellulosic materials. Examples of
common tissue wrapsheet materials include creped wadding or a high
wet-strength tissue. In addition, hydrophilic nonwoven fabrics may
also be used as an absorbent core wrapsheet; see commonly assigned
U.S. Pat. No. 5,458,592 to Abuto et al., the entire contents of
which are incorporated herein by reference.
Separating the absorbent core 16 and the breathable outer cover 12
is a breathable hydrophobic barrier layer 18. In this regard it
has, surprisingly, been found that certain materials will not
appreciably limit the WVTR of the diaper in the dry state yet
significantly decrease the WVTR of the diaper once the absorbent
core has absorbed fluids. Thus, the hydrophobic barrier layer of
the present invention will allow sufficient water vapor
transmission, when the absorbent article is in a dry state, such
that the WVTR of the diaper is not appreciably lowered and the
diaper remains breathable. However, when the absorbent core has
absorbed liquid discharged from the body the hydrophobic barrier
will act to substantially lower the WVTR of the absorbent article
(relative to the same article without a hydrophobic barrier layer),
thereby reducing or eliminating the wet or clammy feeling which may
develop on the outer portion of the backsheet due to
condensation.
The breathable liquid-impervious outer cover 12 and hydrophobic
barrier layer 18 collectively have an inverted-WVTR, as described
herein below, of less than 15,000 g/m.sup.2 /day, desirably less
than about 12,000 g/m.sup.2 /day and still more desirable less than
about 11,000 g/m.sup.2 day. However, the outer cover 12 and
hydrophobic barrier layer 18 have a WVTR over 1500 g/m.sup.2 /day,
desirably over 4000 g/m.sup.2 /day. Although the hydrophobic
barrier layer 18 does not need to have liquid-barrier properties to
the same degree as the liquid-impervious outer covers described
above, it does need to have certain "barrier" like properties in
order to selectively control the WVTR and limit outer cover
dampness. In this regard, suitable materials are those which are
hydrophobic with a hydrohead value of at least 18 cm, preferably
from about 30 cm to about 50 cm. In addition, the hydrophobic
barrier should have a thickness or bulk of at least about 0.012 in.
(0.03 cm), preferably between about 0.018 in. (0.046 cm) to about
0.048 in. (0.122 cm). The hydrophobic barrier layer desirably also
has a Frazier air permeability of at least 20 cubic feet per square
foot per minute (about 6095 liters/square meter/minute) and more
desirably over about 40 ft..sup.3 /ft..sup.2 /min. (about 12192
liters/m.sup.2 /min.).
The hydrophobic barrier layer may comprise breathable fibrous
materials such as a woven or nonwoven fabric having the above
properties, including but not limited to, meltblown webs, fine
fiber spunbond webs such as those having fiber deniers of about 2
or less, bonded and carded webs, hydroentangled fabrics and other
fabrics having the similar properties. Suitable polymeric materials
for making the barrier layer include those capable of making
fibrous webs; examples include but are not limited to polyamides,
polyesters and polyolefins, such as polyethylene and/or
polypropylenes. In a preferred aspect the hydrophobic barrier layer
may comprise a meltblown web of polypropylene fibers having a basis
weight from 16 to about 64 g/m.sup.2, more desirably in excess of
about 20 g/m.sup.2 up to about 40 g/m.sup.2. The fibrous barrier
layer 18 may comprise a single sheet or multiple layered sheets
which collectively have the desired characteristics. However, when
using multiple layered sheets, it is desirable that they be
juxtaposed without being point bonded across a substantial surface
area of the layers or otherwise bonded in a manner which would
substantially limit the breathability of the layers. Similarly, in
a preferred embodiment the hydrophobic barrier layer is not
thermally point bonded or otherwise laminated to the
liquid-impervious outer cover in a manner which destroys the
breathability of the article. In this regard, it may be desirable
that the breathable hydrophobic barrier layer be attached to the
absorbent article primarily at the periphery of the hydrophobic
barrier layer. The multiple layers can be bonded thermally,
ultrasonically, adhesively or by other means known in the art.
In one aspect, as shown in FIG. 1, the hydrophobic barrier sheet 18
may be positioned between the absorbent core 16, which optionally
includes a hydrophilic wrapsheet (not shown), and outer cover 12.
The barrier sheet should extend under at least those regions of the
absorbent core 16 which typically retain the majority of the bodily
discharge. The hydrophobic barrier sheet 18 preferably also extends
under substantially the entire portion of the absorbent core 16 and
may also further extend beyond the edges of the same. As shown in
FIG. 1, the hydrophobic barrier sheet 18 may extend along the
length of the central portion of the diaper 10 underneath the
absorbent core 16. Diaper configurations in which the barrier
extends under the entirety of the absorbent core are highly
preferred where the absorbent core 16 includes a hydrophilic
wrapsheet with good wicking characteristics, such as when using a
tissue core wrap.
In a further aspect, and in reference to FIG. 4, hydrophobic
barrier sheet 18 can comprise one or more layers such as, for
example, a first layer 18a and second layer 18b. The multiple
layers can comprise combinations of materials described herein and
including, but not limited to, meltblown/spunbond and
spunbond/film. Still further, and in reference to FIG. 5,
hydrophobic barrier sheet 18 can itself comprise three layers 18a,
18b, 18c respectively. The multiple layers can include combinations
of materials described herein and including, but not limited to,
spunbond/meltblown/spunbond, spunbond/film/spunbond, and
meltblown/spunbond/meltblown.
In a further aspect of the invention, the barrier layer may
comprise at least a portion of the absorbent core wrapsheet. The
barrier layer may be sufficiently wide so that it may be folded
over on itself and then sealed using, for example, adhesives, heat,
ultrasonic and/or pressure on either the top, bottom or sides of
the wrapsheet. Folding of the barrier layer may be accomplished
through the use of conventional sheet folding means such as curved
plates which work the barrier sheet over onto itself. However, when
a continuous sheet of barrier fabric is used to encapsulate the
absorbent core 16, such as wrapsheet 30, selected portions of the
sheet are preferably treated so that those areas adjacent the
liquid pervious topsheet 14 are hydrophilic. This may be
accomplished by zone treating the barrier layer with a surfactant
to impart wettability to specific areas.
Thus, as shown in FIG. 2, the absorbent core wrapsheet 30 may
comprise a continuous sheet having hydrophilic regions 32 over a
first side of the absorbent core 16 and hydrophobic regions 34 over
the opposite side of the absorbent core 16. When integrated into
the diaper as shown in FIG. 1, the hydrophilic regions would be
facing the liquid pervious topsheet 14 and the opposed hydrophobic
region would comprise at least a portion of the barrier layer.
In an alternate embodiment the absorbent core may have a wrapsheet
30 comprising two or more sheets joined together. For example, as
shown in FIG. 3, the wrapsheet 30 may comprise a hydrophilic liquid
permeable sheet 36 on the side of the absorbent core 12 adjacent
the wearer's side, that is adjacent topsheet 14 of FIG. 1, and a
hydrophobic barrier sheet 38 adjacent the opposed side of the
absorbent core 16. The two sheets 36 and 38 collectively form
wrapsheet 30 and may be sealed by one of various means in the art
such by the use of adhesive, thermal, ultrasonic and/or pressure
bonding.
In addition, the diaper 10, as represented in FIG. 1, may further
include a pair of fasteners 40 which are employed to secure the
diaper 10 about the waist of the wearer (not shown). Suitable
fasteners include hook-and-loop type fasteners, adhesive tape
fasteners, buttons, snaps, mushroom-and-loop fasteners and the
like. Furthermore, although not discussed above, one skilled in the
art will recognize that additional components may be integrally
incorporated within the diaper without departing from the spirit of
the present invention. For example, it is common for diapers to
include elasticized leg bands (not shown) which help secure the
diaper to the wearer and, thus, help reduce leakage from the
diaper. Similarly, it is also known to include a pair of
elasticized, longitudinally extending containment flaps (not shown)
which are configured to maintain a substantially upright,
perpendicular arrangement along the central portion of the diaper
to serve as an additional barrier to the lateral flow of body
exudates. Further, it is also common to include a surge management
layer positioned between the topsheet 14 and the absorbent core 16
in order to help prevent pooling of fluids on the portion of the
diaper adjacent the wearer's skin. These and other components are
well known and the manner and method of using the same in
connection with the absorbent article of the present invention will
likewise be readily appreciated by those skilled in the art.
The various components of the diaper are integrally assembled
together employing various means of attachment known to those
skilled in the art such as, for example, adhesive bonding,
ultrasonic bonds, thermal bonds or combinations thereof.
Test Procedures
Bulk: A measure of the thickness of a fabric. The bulk or thickness
may be determined in accord with ASTM Standard Test Method for
Thickness of Nonwoven Fabrics D 5729-95 using a three inch acrylic
platen which provides 0.05 psi loading.
Hydrohead: A measure of the liquid barrier properties of a fabric
is the hydrohead test. The hydrohead test determines the height of
water or amount of water pressure (in millibars) that the fabric
will support before liquid passes therethrough. A fabric with a
higher hydrohead reading indicates it has a greater barrier to
liquid penetration than a fabric with a lower hydrohead. The
hydrohead can be performed according to Federal Test Standard 191A,
Method 5514. The hydrohead data cited herein was obtained using a
test similar to the aforesaid Federal Test Standard except modified
as noted below. The hydrohead was determined using a hydrostatic
head tester available from Marlo Enterprises, Inc. of Concord, N.C.
The specimen is subjected to a standardized water pressure,
increased at a constant rate until the first sign of leakage
appears on the surface of the fabric in three separate areas.
(Leakage at the edge, adjacent clamps is ignored.) Unsupported
fabrics, such as a thin film, can be supported to prevent premature
rupture of the specimen.
Frazier Permeability: A measure of the permeability of a fabric or
web to air is the Frazier Permeability which is performed according
to Federal Test Standard 191A, Method 5450 dated Jul. 20, 1978, and
is reported as an average of 3 sample readings. Frazier
Permeability measures the air flow rate through a web in cubic feet
of air per square foot of web per minute or CFM. Conversion of CFM
to liters per square meter per minute (LMM) may be accomplished by
multiplying CFM by 304.8.
WVTR: The water vapor transmission rate (WVTR) for the sample
materials was calculated in accordance with ASTM Standard E96-80.
Circular samples measuring three inches in diameter were cut from
each of the test materials and a control which was a piece of
CELGARD2500 film from Hoechst Celanese Corporation of Sommerville,
N.J. CELGARD2500 film is a microporous polypropylene film. Three
samples were prepared for each material. The test dish was a number
60-1 Vapometer pan distributed by Thwing-Albert Instrument Company
of Philadelphia, Pa. One hundred milliliters of water were poured
into each Vapometer pan and individual samples of the test
materials and control material were placed across the open tops of
the individual pans. Screw-on flanges were tightened to form a seal
along the edges of the pan, leaving the associated test material or
control material exposed to the ambient atmosphere over a 6.5
centimeter diameter circle having an exposed area of approximately
33.17 square centimeters. The pans were placed in a forced air oven
at 100.degree. F. (32.degree. C. ) or 1 hour to equilibrate. The
oven was a constant temperature oven with external air circulating
through it to prevent water vapor accumulation inside. A suitable
forced air oven is, for example, a Blue M Power-O-Matic 60 oven
distributed by Blue M. Electric Company of Blue Island, Ill. Upon
completion of the equilibration, the pans were removed from the
oven, weighed an immediately returned to the oven. After 24 hours,
the pans were removed from the oven and weighed again. The
preliminary test water vapor transmission rate values were
calculated with Equation (I) below:
The relative humidity within the oven was not specifically
controlled.
Under the predetermined set conditions of 100.degree. F.
(32.degree. C.) and ambient relative humidity, the WVTR for the
CELGARD2500 control has been defined to be 5000 grams per square
meter for 24 hours. Accordingly, the control sample was run with
each test and the preliminary test values were corrected to set
conditions using Equation (II) below:
Inverted WVTR: This test is similar to the WVTR discussed above
with the exception that the cup is inverted such that the water
contacts the fabric being tested. In addition, since the WVTR of
CELGUARD 2500 is not 5000 g/m.sup.2 /24 for the inverted test, this
control and correction has been deleted from the calculations of
the inverted water vapor transmission rate test. This test is
believed to more accurately duplicate the vapor transfer
experienced by a loaded absorbent article.
EXAMPLE 1
A propylene meltblown fiber nonwoven web was made using Himont
PF-015 polypropylene polymer from Himont, USA of Wilmington, Del.
The meltblown web was made in accordance with meltblowing
techniques described in U.S. Pat. No. 5,458,592 using a multiple
bank meltblown apparatus. The polypropylene was extruded through a
multiple bank meltblown die assembly at a throughput of 2.5 pounds
per inch per hour (PIH). The extruded streams of molten polymer
were attenuated with primary attenuation air delivered at a rate of
between about 1700 and 2000 cubic feet per minute at a temperature
of 530.degree. F. The resultant meltblown had a basis weight of 8.0
grams per square meter (g/m.sup.2) and a bulk of 0.006 inches
(0.015 cm). The mean flow pore size for the sample was about 25
microns and the maximum flow pore size was 47 microns with 0.5
percent of the overall pores having a pore size greater than 50
microns. The web had a supported hydrohead of 17.6 mbar, an
unsupported hydrohead of 19.5 mbar and Frazier air permeability of
287 cubic feet per square foot per minute (CFM). A sample of the
meltblown web was subsequently juxtaposed with a 0.0025 cm thick
film of CELGUARD 2500, without bonding or otherwise laminating the
materials together. The breathable liquid-impermeable film and
meltblown layer collectively had a WVTR of 5154 g/m.sup.2 /day and
an inverted-WVTR of 19396 g/m.sup.2 /day.
EXAMPLE 2
A nonwoven web of polypropylene meltblown fibers, as described
above in Example 1, was also used in the present example. Three
plies of the nonwoven web were juxtaposed, without bonding or
otherwise laminating the layers, an d had a collective bulk of
0.012 inches (0.03 cm), supported hydrohead of 37.7 mbar, an
unsupported hydrohead of 37.4 mbar and a Frazier Air Permeability
of 81.4 CFM. The 3 ply layer of nonwoven material was then
juxtaposed over a breathable liquid-impervious barrier of 0.0025 cm
thick film of CELGUARD 2500. The breathable film and nonwoven layer
collectively had a WVTR of about 5154 g/m.sup.2 /day and an
inverted-WVTR of 10367 g/m.sup.2 /day.
EXAMPLE 3
A nonwoven web of polypropylene meltblown fibers, as described
above in Example 1, was also used in the present example. Five
plies of the nonwoven were juxtaposed, without bonding or otherwise
laminating the layers, and had a collective bulk of 0.017 inches
(0.04 cm), supported hydrohead of 50.5 mbar, an unsupported
hydrohead of 46.1 mbar and a Frazier Air Permeability of 81.4 CFM.
The five ply layer of nonwoven material was subsequently juxtaposed
over a breathable liquid-impervious barrier of 0.0025 cm thick film
of CELGUARD 2500 without bonding or otherwise laminating the
respective materials. The breathable film and nonwoven layer
collectively had a WVTR of about 4528 g/m.sup.2 /day and an
inverted-WVTR of 12055 g/m.sup.2 /day.
EXAMPLE 4
A spunbond material was made in accord with the teachings described
herein above resulting in a 0.5 osy (17 g/m.sup.2) web of
continuous spunbond fibers. The spunbond layer was juxtaposed with
two layers of meltblown webs of Example 1 such that the spunbond
layer was positioned between the two meltblown layers. The
meltblown/spunbond/meltblown material was not bonded or otherwise
laminated together. The 3 ply layer had a bulk of 0.016 inches
(0.04 cm), supported hydrohead of 38.0 mbar, an unsupported
hydrohead of 39.7 mbar and Frazier Air Permeability of 112.4 CFM.
The 3 ply layer of nonwoven material was then juxtaposed over a
breathable liquid-impervious barrier of 0.0025 cm thick film of
CELGUARD 2500 without bonding or otherwise laminating the
respective-materials. The breathable liquid-impervious film and
nonwoven layers collectively had a WVTR of about 4609 g/m.sup.2
/day and an inverted-WVTR of 10739 g/m.sup.2 /day.
EXAMPLE 5
A meltblown web made in of Example 1 was juxtaposed with two
spunbond webs of Example 4 such that the meltblown web was
positioned between the two spunbond layers. The 3 ply layer had a
bulk of 0.019 inches (0.05 cm) supported hydrohead of 27.4 mbar, an
unsupported hydrohead of 29.3 mbar and Frazier Air Permeability of
181 CFM. The 3 ply layer was subsequently juxtaposed with an 0.0025
cm thick film of CELGUARD 2500 without bonding or laminating the
respective materials. The breathable liquid-impermeable film and 3
ply layer collectively had a WVTR of 4415 g/m.sup.2 /day and an
inverted-WVTR of 11,486 g/m.sup.2 /day.
EXAMPLE 6
A 0.0025 cm thick film of CELGUARD 2500 was juxtaposed with two
layers of spunbond fibers of Example 4 such that the breathable
film was between the two spunbond layers. The 3-ply layer had a
bulk of 0.018 inches (0.046 cm), supported hydrohead of 206.8 mbar,
an unsupported hydrohead of 190.9 mbar and Frazier Air Permeability
of 0.172 CFM. The 3 ply layer was subsequently juxtaposed with an
0.0025 cm thick film of 0.0025 cm thick film of CELGUARD 2500
without bonding or otherwise laminating the respective materials
together. The breathable film and 3 ply layer collectively had a
WVTR of 4652 g/m.sup.2 /day and an inverted-WVTR of 12,315
g/m.sup.2 /day.
As may be appreciated by the foregoing examples, it has been
surprisingly found that certain materials have little effect on the
WVTR of an absorbent article when dry yet significantly reduce the
WVTR of the absorbent article when loaded. In reference to Example
1, the 0.006 thick meltblown material, in conjunction with the
CELGUARD 2500, had an excellent WVTR of 5153 CFM and a
correspondingly high inverted-WVTR of 19396 CFM. However, the
multiply meltblown layer having a bulk of about 0.012 inches (0.03
cm) also had a good WVTR of 4807 CFM. However, the inverted-WVTR of
Example 2 was but 10376 CFM. Thus, the bulkier meltblown, while not
appreciably limiting the WVTR, dramatically reduced the
inverted-WVTR relative to both the control and Example 1 by about
50%. Accordingly, an absorbent article employing such a barrier
layer would have the desired breathability when dry yet would have
a reduced WVTR when the article is loaded, thereby reducing or
eliminating outer over dampness caused by condensation. Comparable
results are obtained by other material layers with the requisite
functional characteristic described herein above. Further, as shown
in Example 6, these results are comparable to those employing a
second breathable liquid-impervious layer. However, one skilled in
the art will appreciate that the high costs associated with
breathable liquid-impervious covers, such as microporous films, may
be avoided with the absorbent articles of the present
invention.
While the invention has been particularly shown and described with
reference to preferred embodiments thereof, it will be understood
by those skilled in the art that other changes in form and details
may be made therein without departing from the spirit and scope of
the invention.
* * * * *